If I use caffeine to improve my performance, how much should I use?
Caffeine in moderate doses can boost both physical and mental performance. It can help maintain alertness during long activities such as patrolling at night or when you are sleep deprived. However, if you can, it is better to get the sleep your body needs. The amount of caffeine that can help performance is up to 200 mg (about the amount of caffeine in 8 to 12 oz. of brewed coffee). Caffeine should be consumed about 30–60 minutes before a workout, training session, work shift, or mission for best results, as it takes about 45–60 minutes to reach peak blood levels. That also means you might need another dose of caffeine after 3–4 hours to help you stay alert or active for a long period of time.
Doses higher than 200 mg can cause side effects such as nervousness, irritability, and shakiness. More caffeine will not improve your performance, and the various negative side effects of higher doses might actually make it worse.
Importantly, you should not consume caffeine before trying to sleep. As peak blood levels of caffeine last for up to 3–4 hours after ingestion, try to avoid caffeine for at least 6 hours before bedtime to make sure it doesn't interfere with your sleep.
FAQ updated 13 May 2016